Corrosion protection by anaerobiosis

Biofilm-forming bacteria can protect mild (unalloyed) steel from corrosion. Mild steel coupons incubated with Rhodoccocus sp. strain C125 and Pseudomo nas putida mt2 in an aerobic phosphate-buffered medium containing benzoate as carbon and energy source, underwent a surface reaction leading to the fo rmation of a corrosion-inhibiting vivianite layer [Fe-3(PO4)(2)]. Electroch emical potential (E) measurements allowed us to follow the buildup of the v ivianite cover. The presence of sufficient metabolically active bacteria at the steel surface resulted in an E decrease to -510 mV, the potential of f ree iron, and a continuous release of ferrous iron. Part of the dissolved i ron precipitated as vivianite in a compact layer of two to three microns in thickness. This layer prevented corrosion of mild steel for over two weeks , even in a highly corrosive medium. A concentration of 20 mM phosphate in the medium was found to be a prerequisite for the formation of the vivianit e layer.